Portions of the present disclosure are contained within U.S. Pat. No. 6,919,042 which is hereby expressly incorporated by reference in its entirety. The present disclosure particularly relates to an improved oxidation and fatigue resistant metallic coating for protecting high temperature gas turbine engine components.
Various metallic coatings have been developed in the past for the oxidation protection of high temperature gas turbine engine components. These coatings are often based on different aluminide compositions, and may include nickel or cobalt base metal materials. Alternatively, they are based on overlay deposits with MCrAlY foundations where M is nickel, cobalt, iron or combinations of these materials. These coating systems suffer from shortcomings that preclude their use on newer advanced turbine components. The diffused aluminides, while possessing good fatigue resistance, generally provide lower high temperature oxidation resistance (above 2000 degrees Fahrenheit). The overlay MCrAlY coatings tend to have tensile internal stress, which can promote cracking and reduces the fatigue life of the coating (i.e. creates fatigue debt). The addition of active elements to the MCrAlY coatings not only provides excellent oxidation resistance, but makes them good candidates for bond-coats for thermal barrier coatings.
Thermal barrier coating systems (TBCs) provide a means to protect the turbine engine components from the highest temperatures in the engine. Before a TBCs is applied, metallic bond coats, such as aluminides or MCrAlY coatings, are deposited on the surface of the turbine engine component, and a thermally grown oxide of alumina is grown between the bond coat and the TBCs topcoat.
As superalloy technology advances, the economics and material trade-offs involved in creating creep resistant higher refractory-containing super alloys have become of interest. While both aluminides and MCrAlY coatings have widespread applications, a low-cost improved coating that could combine the best properties from both would have immediate application on advanced turbine components where fatigue, pull weight, and oxidation must all be minimized.